Lee> So, on to my issue de jour. What (if any) effect have you seen of geologic
processes in your projects? Have streambeds changed due to erosion? How about entire
watersheds? DNR geologists here in GA tell me that in the "peidmont" region of
state, streambeds may change (to a minor degree) but the watersheds shouldn't.
John> It takes a mighty heave of Nature - or geologic time - to change watersheds.
But one can see in the Mississippi - easiest on Landsat imagery - the dramatic
influence of old floods (and probably earthquakes like the amazing New Madrid event
early in the 19th century) on the River course, with old oxbows now prime bottom land,
but still very visible from above. The Corps of Engineers has slowed this process
down - or at least changed how Nature gets her licks in.
Or read Mark Twain's classic, "Life on the Mississippi" based on his own
as a Mississippi River pilot. There were frequent enough changes in the River BETWEEN
pilot trips to cause maritime disasters for untalented or unlucky pilots. I think
river pilots in those days had about the same life expectancy as (flight) test pilots
I would expect that the main engine of inland streambed change, whether we are talking
about huge rivers or the kinds of minor creeks we mostly encounter in our deeds, is
over-the-top flooding. You might call this hyper-accelerated erosion. Where the
stream emanates from steep or extensive hills or mountains, flash floods might be
capable of precipitating the same kinds of cataclysmic events that bedevilled the
Mississippi River pilots - on a smaller scale, of course. The other parameter is
whether there are alternate channels for such a stream. If it runs through a fairly
steep dip or gorge, it's probably going to be following the same path 300 years from
now, regardless of natural events.
Of course there are man-made events, like the damming of the S Fork of the Holston, or
of the Little Calfpasture River, the site of my other deedmapping project. Or, as far
as that goes, I live about 20 minutes from Smith Mountain Lake, VA, where they
obliterated a whole 30 mile valley system in the 1950s by damming the Roanoke River at